Differential oil change clunking noise

[TJPark01]

I changed the diff oil on a 1995 Lexus LS400 w/135k miles on it. The oil has never been changed and the diff was functioning perfectly. I used the specified 80W-90 Gear Oil.
Now when I drive at 40-50mph and let go of the gas the back end makes a clunking noise and shakes the back end. Only under this driving speed, other times it works fine. [censored]?

 

[abycat]

Does it need a limited slip additive?

 

[TJPark01]

Originally Posted By: abycat
Does it need a limited slip additive?

It's a 17 year old car. I don't think it has a LSD.

 

[Rand]

Is it possible you are only noticing it now? I dont see how the oil would make any sort of clunking noise difference by itself.

 

[Chris142]

Originally Posted By: TJPark01
Originally Posted By: abycat
Does it need a limited slip additive?

It's a 17 year old car. I don't think it has a LSD.
Why wouldn't it? LSD rear ends are not something new. Clutch type of Posi's go back into the 60's or earlier.

My 68 Scout and 73 Duster both had em from the factory.

 

[JHZR2]

^this.

If any car is going to come OE with an LSD it is a nice older LS.

 

[law3500]

Originally Posted By: TJPark01
Originally Posted By: abycat
Does it need a limited slip additive?

It's a 17 year old car. I don't think it has a LSD.


Many LS400's have LSD.

 

[SS1970chrysler]

My '59 Ford and edsels all had them from the factory. You might be able to just add a limited-slip additive to the oil you just used instead of dumping it.

 

[Chris142]

Originally Posted By: law3500
Originally Posted By: TJPark01
Originally Posted By: abycat
Does it need a limited slip additive?

It's a 17 year old car. I don't think it has a LSD.


Many LS400's have LSD.
Yup. I bet that if he put one wheel on street and one in dirt then gassed it he would see that it has a posi.

 

[aquariuscsm]

Try a different oil and see if it fixes it. What kind did you use?

 

[JHZR2]

I probably would have run M1 75w-90 or Amsoil CVG 75w-90 in there, all of which have the add mixed in.

No reason not to run syn diff fluid, IMO.

 

[TJPark01]

Originally Posted By: aquariuscsm
Try a different oil and see if it fixes it. What kind did you use?


Valvoline 80w-90 gear oil.

 

[antonmnster]

LSD problems would only manifest themselves when turning, generally tight turns at low speeds.

A clunk like that might be more along the lines of a failed flex disc. I believe there are two on this drive shaft, one at each end. Or maybe a bad bushing on the diff carrier or rear subframe.

 

[TJPark01]

Originally Posted By: antonmnster
LSD problems would only manifest themselves when turning, generally tight turns at low speeds.

A clunk like that might be more along the lines of a failed flex disc. I believe there are two on this drive shaft, one at each end. Or maybe a bad bushing on the diff carrier or rear subframe.


why does this only happen at 40-50 mph? Is it worth changing the oil again to a synthetic type?

 

[JHZR2]

Are you sure you closed everything up, everything is tight, didnt jack up the car the wrong way, effect the driveshaft balance, etc.?

 

[TJPark01]

Originally Posted By: JHZR2
Are you sure you closed everything up, everything is tight, didnt jack up the car the wrong way, effect the driveshaft balance, etc.?


Yes. I know you have to ask because you don't know the level of sophistication with people on this site. But trust me when I say I have the dealer service manual, more tools than any one person needs and a high level of competence. I've done all the work myself on this car, brakes,plugs,oil changes,filters,all fluids.

 

[HTSS_TR]

My 1994 LS400 with 270+k miles has M1 75W90 for more than 80-90k miles without problem you have.

 

[Jim Allen]

I have 1916 papers and photos from a well known truck manufacturer that tested some of the available limited slips/locking differentials of the day for possible use in their trucks. I found ads from 1913 and evidence that at least one LSD existed in 1905. Some of the more famous names in that era were the Luxmore, the Scurlock, the Walter, the Dorr-Miller,the Brown-Lipe and the M&S. DeLavaud invented a plate type diff in 1938 but as far as I know, the '55 Packard was the first mass produced car to offer a factory installed, clutch type limited slip in the form of the Lyeth Engineering developed Powr-Lok (later to become the Spicer Powr-Lok).